Magnetic rotation-angle detector

Abstract

Provided is a magnetic rotation-angle detector that includes a disk-shaped magnet that is magnetized so as to change magnetic poles n times per rotation (where n is an integer equal to or larger than 1); a magnetic-body slit plate that is rotated together with the magnet, where a part having a high magnetic flux permeability and a part having a low magnetic flux permeability are alternately and repeatedly arranged thereon so as to change the magnetic flux permeability m times per rotation (where m is an integer equal to or larger than 2 and m>n); a magnetic sensor that detects magnetism from the magnet when the magnet has passed by through the magnetic-body slit plate; and a calculation unit that obtains the rotation angle of the magnet from the output from the magnetic sensor.

The invention claimed is: 
     
       1. A magnetic rotation-angle detector comprising:
 a magnetic sensor in which magnetic detection elements are arranged with a space of π/n [rad], where n is an integer equal to or larger than 1; or π/m [rad], where m is an integer equal to or larger than 2, and m>n therebetween and that separates and takes a signal of a rotation period of m or a rotation period of n from a magnetic field change in which the rotation period of m and the rotation period of n are superimposed; 
 a rotating disk-shaped magnet that is magnetized so as to present, to the magnetic sensor, a complete 360 degree cycle of magnetic polarity change n times per rotation; 
 a unit, comprising a magnetic-body slit plate that is rotated together with the magnet, that generates a magnetic filed change in which a rotation period of m and a rotation period of n are superimposed per rotation of the unit, the magnetic-body slit plate that is rotated together with the magnetic-body slit plate being provided with a part having a high magnetic flux permeability and a part having a low magnetic flux permeability that are alternately and repeatedly arranged thereon, so as to cycle a magnetic flux permeability m times per rotation; and 
 a calculator unit that separates a signal component having a frequency of n and a signal component having a frequency of m from an output from the magnetic sensor and obtains a rotation angle of the magnet. 
 
     
     
       2. The magnetic rotation-angle detector according to  claim 1 , wherein
 a non-magnetic body spacer is provided between the magnet and the magnetic-body slit plate, and 
 a fixed space is provided between the magnet and the magnetic-body slit plate. 
 
     
     
       3. The magnetic rotation-angle detector according to  claim 1 ,
 further comprising a disk-shaped second magnet that is provided on an inner side of the magnet and that is magnetized so as to present, to the magnetic sensor, a complete 360 degree cycle of magnetic polarity k times per rotation, where k is an integer equal to or larger than 1, and k<n. 
 
     
     
       4. The magnetic rotation-angle detector according to  claim 1 , wherein
 the magnetic-body slit plate is formed by printing a magnetic ink on a surface of the magnet.